The loss of sensory hair cells is a leading cause of deafness in humans. Although the mammalian inner ear is unable to replace lost or damaged hair cells, birds and other non-mammalian vertebrates can regenerate hair cells (HC) after injury. Regeneration is mediated by supporting cells, which can either divide or trans-differentiate into replacement HCs. Characterization of the mechanisms that permit avian HC regeneration can inform and guide approaches to induction of similar regeneration in the human ear. Canonical Wnt signaling has been shown to regulate tissue homeostasis and regeneration in progenitor/stem cell populations in many somatic tissues, and also plays a role in the embryonic development of the inner ear. Our preliminary data reveal a critical and unexpected role for Wnt signaling in the basilar papillae (BP) of post-hatch chicks. Specifically, we have found that small molecule inhibition of the Wnt/-catenin signaling pathway induces high levels of cell cycle entry in cochlear supporting cells. Based on this finding, we propose to: (1) quantif changes in supporting cell proliferation and gene expression in response to treatment with various modulators of Wnt/-catenin signaling, (2) identify possible downstream signals that result from Wnt inhibition, and (3) to characterize the effects of Wnt modulation in the developing mouse organ of Corti. The outcome of these experiments will clarify the role of canonical Wnt signaling in the cochleae of birds and mammals and will enhance our understanding of the processes that regulate sensory regeneration. PUBLIC HEALTH RELEVANCE: The National Institutes of Health estimates that at least thirty-six million Americans and thirty to fifty percent of retired seniors suffer from some degree of hearing loss, and that nearly three out of every thousand children born in the United States are deaf or hard-of-hearing. A large percentage of this population suffers from permanent hearing impairment due to loss of inner ear sensory hair cells that, as in all mammals, lack the capacity to regenerate. The proposed projects outlined herein describe our study of chicken inner ear sensory hair cells, which spontaneously regenerate after loss, to guide our efforts in developing therapies for hearing loss and deafness via human hair cell regeneration.